// Part 2 about an Interpreter for the Brainf*** language

//========================================================

object CW8b {

type Mem = Map[Int, Int]

// (2a) Complete the functions for safely reading  

// and writing brainf*** memory. Safely read should

// Return the value stored in the Map for a given memory

// pointer, if it exists; otherwise it Returns 0. The

// writing function generates a new Map with the

// same data, except at the given memory pointer the

// value v is stored.

def sread(mem: Mem, mp: Int) : Int = 

  mem.getOrElse(mp, 0)

def write(mem: Mem, mp: Int, v: Int) : Mem =

  mem.updated(mp, v)

// (2b) Implement the two jumping instructions in the 

// brainf*** language. In jumpRight, given a program and 

// a program counter move the program counter to the right 

// until after the *matching* ]-command. Similarly, 

// jumpLeft implements the move to the left to just after

// the *matching* [--command.

def jumpRight(prog: String, pc: Int, level: Int) : Int = {

  if (prog.length <= pc) pc 

  else (prog(pc), level) match {

    case (']', 0) => pc + 1

    case (']', l) => jumpRight(prog, pc + 1, l - 1)

    case ('[', l) => jumpRight(prog, pc + 1, l + 1)

    case (_, l) => jumpRight(prog, pc + 1, l)

  }

}

def jumpLeft(prog: String, p: Int, level: Int) : Int = {

  if (p < 0) p 

  else (prog(p), level) match {

    case ('[', 0) => p + 1

    case ('[', l) => jumpLeft(prog, p - 1, l - 1)

    case (']', l) => jumpLeft(prog, p - 1, l + 1)

    case (_, l) => jumpLeft(prog, p - 1, l)

  }

}

// (2c) Complete the run function that interpretes (runs) a brainf***

// program: the arguments are a program, a program counter,

// a memory counter and a brainf*** memory. It Returns the

// memory at the stage when the excution of the brainf*** program

// finishes. The interpretation finishes once the program counter

// pc is pointing to something outside the program string.

// If the pc points to a character inside the program, the pc, 

// memory pointer and memory need to be updated according to 

// rules of the brainf*** language. Then, recursively, run 

// function continues with the command at the new program

// counter. 

// Implement the start function that calls run with the program

// counter and memory counter set to 0.

def run(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = {

  if (0 <= pc && pc < prog.length) { 

    val (new_pc, new_mp, new_mem) = prog(pc) match {

      case '>' => (pc + 1, mp + 1, mem)

      case '<' => (pc + 1, mp - 1, mem)

      case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))

      case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))

      case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }

      case ',' => (pc + 1, mp, write(mem, mp, Console.in.read().toByte))

      case '['  => 

	if (sread(mem, mp) == 0) (jumpRight(prog, pc + 1, 0), mp, mem) else (pc + 1, mp, mem) 

      case ']'  => 

	if (sread(mem, mp) != 0) (jumpLeft(prog, pc - 1, 0), mp, mem) else (pc + 1, mp, mem) 

      case _ => (pc + 1, mp, mem)

    }		     

    run(prog, new_pc, new_mp, new_mem)	

  }

  else mem

}

def start(prog: String, m: Mem) = run(prog, 0, 0, m)

// some sample programs collected from the Internet

//==================================================

/*

// first some contrived (small) programs

// clears the 0-cell

start("[-]", Map(0 -> 100)) 

// copies content of the 0-cell to 1-cell

start("[->+<]", Map(0 -> 10))

// copies content of the 0-cell to 2-cell and 4-cell

start("[>>+>>+<<<<-]", Map(0 -> 42))

// prints out numbers 0 to 9

start("""+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]""", Map())

// some more "useful" programs

// hello world program 1

start("""++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++

       ..+++.>>.<-.<.+++.------.--------.>>+.>++.""", Map())

// hello world program 2

start("""++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>+

      +.<<+++++++++++++++.>.+++.------.--------.>+.>.""", Map())

// draws the Sierpinski triangle

start("""++++++++[>+>++++<<-]>++>>+<[-[>>+<<-]+>>]>+[-<<<[

      ->[+[-]+>++>>>-<<]<[<]>>++++++[<<+++++>>-]+<<++.[-]<<

      ]>.>+[>>]>+]""", Map())

//fibonacci numbers below 100

start("""+++++++++++

      >+>>>>++++++++++++++++++++++++++++++++++++++++++++

      >++++++++++++++++++++++++++++++++<<<<<<[>[>>>>>>+>

      +<<<<<<<-]>>>>>>>[<<<<<<<+>>>>>>>-]<[>++++++++++[-

      <-[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]>[<<[>>>+<<<

      -]>>[-]]<<]>>>[>>+>+<<<-]>>>[<<<+>>>-]+<[>[-]<[-]]

      >[<<+>>[-]]<<<<<<<]>>>>>[+++++++++++++++++++++++++

      +++++++++++++++++++++++.[-]]++++++++++<[->-<]>++++

      ++++++++++++++++++++++++++++++++++++++++++++.[-]<<

      <<<<<<<<<<[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<-[>>.>.<<<

      [-]]<<[>>+>+<<<-]>>>[<<<+>>>-]<<[<+>-]>[<+>-]<<<-]""", Map())

//outputs the square numbers up to 10000

start("""++++[>+++++<-]>[<+++++>-]+<+[

    >[>+>+<<-]++>>[<<+>>-]>>>[-]++>[-]+

    >>>+[[-]++++++>>>]<<<[[<++++++++<++>>-]+<.<[>----<-]<]

    <<[>>>>>[>>>[-]+++++++++<[>-<-]+++++++++>[-[<->-]+[<<<]]<[>+<-]>]<<-]<<-]""", Map())

//collatz numbers (need to be typed in)

start(""">,[[----------[

      >>>[>>>>]+[[-]+<[->>>>++>>>>+[>>>>]++[->+<<<<<]]<<<]

      ++++++[>------<-]>--[>>[->>>>]+>+[<<<<]>-],<]>]>>>++>+>>[

      <<[>>>>[-]+++++++++<[>-<-]+++++++++>[-[<->-]+[<<<<]]<[>+<-]>]

      >[>[>>>>]+[[-]<[+[->>>>]>+<]>[<+>[<<<<]]+<<<<]>>>[->>>>]+>+[<<<<]]

      >[[>+>>[<<<<+>>>>-]>]<<<<[-]>[-<<<<]]>>>>>>>

      ]>>+[[-]++++++>>>>]<<<<[[<++++++++>-]<.[-]<[-]<[-]<]<,]""", Map())

// infinite collatz (never stops)

start(""">>+>+<[[->>[>>]>>>[>>]+[<<]<<<[<<]>[>[>>]>>+>[>>]<+<[<<]<<<[<

      <]>-]>[>>]>>[<<<<[<<]>+>[>>]>>-]<<<<[<<]+>>]<<[+++++[>+++++++

      +<-]>.<++++++[>--------<-]+<<]>>[>>]+[>>>>[<<+>+>-]<-[>+<-]+<

      [<<->>-[<<+>>[-]]]>>>[<<<+<<+>>>>>-]<<<[>>>+<<<-]<<[[-]>+>>->

      [<+<[<<+>>-]<[>+<-]<[>+<-]>>>>-]<[>+<-]+<[->[>>]<<[->[<+++>-[

      <+++>-[<+++>-[<[-]++>>[-]+>+<<-[<+++>-[<+++>-[<[-]+>>>+<<-[<+

      ++>-[<+++>-]]]]]]]]]<[>+<-]+<<]>>>+<[->[<+>-[<+>-[<+>-[<+>-[<

      +>-[<+>-[<+>-[<+>-[<+>-[<[-]>>[-]+>+<<-[<+>-]]]]]]]]]]]<[>+<-

      ]+>>]<<[<<]>]<[->>[->+>]<[-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<-

      >>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>-[<->>+<-[<+>

      -[<->>+<-[<+>-[<->>+<-[<+>-]]]]]]]]]]]]]]]]]]]>[<+>-]<+<[<+++

      +++++++>-]<]>>[<+>->>]<<[>+>+<<-]>[<+>-]+>[<->[-]]<[-<<-]<<[<

      <]]++++++[>+++++++<-]>++.------------.[-]>[>>]<<[+++++[>+++++

      +++<-]>.<++++++[>--------<-]+<<]+<]>[<+>-]<]>>>[>>]<<[>[-]<-<

      <]++++++++++.[-]<<<[<<]>>>+<[->[<+>-[<+>-[<+>-[<+>-[<+>-[<+>-

      [<+>-[<+>-[<+>-[<[-]>>[-]+>+<<-]]]]]]]]]]<[>+<-]+>>]<<[<<]>>]""", Map())

*/ 

}